1. Field of the Invention
The present invention relates to a process for protecting nonstable or moderately stable, cohesions to slightly cohesive geologic formations, in particular, in tunnel construction, in which drill holes are first made in the formation and, following completion of the borings, the drilling rods are removed, and a hardenable injection material is forced into the drill hole, during the removal.
2. The Prior Art
In cavity construction, extended drilling in soft or unconsolidated rock is either avoided or executed by means of costly machinery such as shields, hydroreinforced breasts or the like or by means of extensive injection procedures or freezing methods.
An additional complex and expensive process comprises the combination of compressed air and the new Austrian method of tunnel construction. These processes have the drawback that expensive mechanical means are required for their implementation. Especially with shorter tunnels or in the eventuality that only smaller sections of a longer tunnel require more labor- and cost-intensive reinforcement measures owing to the presence of unconsolidated rock, utilization of such processes is not justified by the attendant expense.
Injection boring anchors and preliminary breast boards with preliminary breast sheets, preliminary breast pointed bars and the like constitute another variation of advance protection known in the art. These safety provisions can be set up on site with relatively low equipment costs. A drawback of the injection boring anchor is the fact that the drill bit remains together with the anchoring element inside the borehole and is consequently lost. This results in relatively high consumption of expensive materials.
In addition, injection bar methods (alluvial pointed bars) are known in the art according to which, following construction of the borehole, the drilling rod is removed from the drill hole and an anchoring element or pointed bar inserted which is cast into the borehole by means of a hardenable injection material. This process exhibits the disadvantage that several operation cycles are required for its implementation, with the result that work progress is necessarily slow. Additionally, the drill hole can collapse between the removal of the drilling rod and introduction of the alluvial pointed bar, necessitating additional time consuming operations.